This application is entitled to the benefit of and incorporates by reference essential subject matter disclosed in Japanese Patent Application No. 2001-183487 filed Jun. 18, 2001.
1. Field of the Invention
The present invention relates to a warm-up control method for an electronically controlled engine which is installed in vehicles and the like.
2. Description of the Related Art
Generally in electronically controlled engines installed in vehicles and the like, fast idle control for raising the number of idle revolutions higher than the ordinary number of revolutions is executed to enhance warm-up after the engine has been started up. In other words, as is shown in FIG. 6, from the time of engine start-up until the water temperature reaches a prescribed temperature, the amount of fuel injection supplied to the engine is greater than the amount corresponding to the ordinary number of idle revolutions Ni, and control is conducted so as to raise the number of engine revolutions higher than the ordinary number of idle revolutions Ni. The main parameter that determines the number of fast idle revolutions Nf is water temperature, and other parameters such as intake-air temperature may also be included. In the example shown in the drawings, control is carried out whereby for a prescribed period of time after engine start-up the maximum number of fast idle revolutions Nfmax is maintained, and thereafter, as the water temperature rises, the number of fast idle revolutions Nf is gradually lowered, and eventually the ordinary number of idle revolutions Ni is reached.
However, when this kind of fast idle control is carried out in an in-cylinder injection engine in which fuel is injected directly into a cylinder, the wall surface temperature of the piston has not yet risen sufficiently immediately after start-up, and so fuel that adheres to the piston wall surface when injected into the cylinder does not evaporate and is discharged outside the cylinder in that state, leading to the emission of a large amount of white smoke. Moreover, since the number of engine revolutions is set high during fast idle control, an even greater amount of white smoke is emitted.
Consequently, the present invention was designed with the foregoing problems in view, and it is an object thereof to reduce the amount of white smoke emitted immediately after start-up.
The present invention is a method for executing engine warm-up control using electronic control units, wherein start-up idle control, which does not perform the prescribed fast idle control is carried out until a prescribed period of time has elapsed after engine start-up, whereupon the fuel injection amount is increased and fast idle control is executed.
Immediately after engine start-up, start-up idle control is carried out to restrict the fuel injection amount to a value nearly corresponding to the number of idle revolutions. Since this is lower than during fast idle control, a situation in which there is a large amount of fuel injection and a high number of revolutions while the piston wall surface temperature is still low is prevented, and the amount of white smoke emitted can be significantly reduced.
Further, the present invention is a method for performing engine warm-up control using electronic control units, wherein start-up idle control for setting the fuel injection amount at a level producing the minimum amount of white smoke emissions, is executed until a prescribed period of time has elapsed after engine start-up, whereupon the fuel injection amount is increased, and fast idle control is executed.